Reducing the shrinkage stress of epoxy resin
The shrinkage stress of thermal cured epoxy resin developed during curing process can cause low film adhesion strength, low dimensional accuracy and even coating films warping which severely reduce service lifetime of the coating. Therefore, there is growing interest in developing effective means to reduce the shrinkage stress. In a new paper, researchers report the use of hollow microspheres prepared from Pickering emulsion droplets in the thermal cured epoxy resin formulations. Epoxy group functionalised silica nanoparticles from the Stöber method were used as Pickering emulsion stabiliser and the emulsion droplets are polymerized to obtain hollow microspheres with controllable mechanical properties and surface morphologies. Due to the reactivity of the hollow microspheres, they can be incorporated into the epoxy resin coatings and the shrinkage stress is thus reduced.
Test results revealed that the shrinkage stress was reduced from 195.79 kPa to 140. 40 kPa with the addition of 12 wt% hollow microspheres and polydisperse hollow microspheres are more effective in shrinkage stress reduction. As the modulus of the hollow microspheres is reduced and elasticity is increased, the shrinkage stress of the coating film is also reduced from 181. 37 kPa to 157.42 kPa which is not achieved by hollow glass microspheres. The hollow microspheres are well dispersed in the resin matrices which doesn’t undermine the basic mechanical properties of the coating such as adhesion and surface hardness.
The study has been published in Progress in Organic Coatings, Volume 178, May 2023.